Carborundum—Carborundum is the hardest surface made by humans and is second only to the diamond's hardness. Acheson created carborundum (silicon-carbide) by electronically fusing clay and carbon. His invention resulted in a search for a highly effective and durable abrasive needed by industry to manufacture precision-ground interchangeable metal parts. A by-product of carborundum was graphite, which proved to be useful as a lubricant. The U.S. Patent Office once named this discovery as one of the inventions most responsible for the industrial age. (1997)